Swash plate pumps and motors



Jan- 14, 1 4 D. FIRTH ETAL 3,117,529

SWASH PLATE PUMPS AND MOTORS Filed Jan. 16, 1961 3 Sheets-Sheet l Jan. 14, 1964 D. FIRTH ETAL 2 SWASH PLATE PUMPS AND MOTORS Filed Jan. 16, 1961 5 Sheets-Sheet 2 Jan. 14, 1964 D. FIRTH ETAL SWASH PLATE PUMPS AND MOTORS 3 Sheets-Sheet 5 Filed Jan. 16, 1961 United States Patent 3,117,529 SWASH PLATE PUMPS AND MOTORS Donald Firth and Roger Harvey Yorke Hancock, Glasgo'w, Scotland, assignors to Council For Scientific and Industrial Research, London, England, a corporation of the United Kingdom Filed Jan. 16, 1961, Ser. No. 83,089 Claims priority, application Great Britain Jan. 23, 1960 2 tllaims. (Cl. 103-162) This invention relates to hydraulic machines and particularly to swash plate pumps and motors of the kind comprising a rotatable cylinder block which has a number of cylinders containing pistons reciprocab-le under the control of a stationary swash plate and which has ports in a flat face thereof communicating with said cylinders and co-operating with inlet and outlet ports in a flat face of a stationary port block. Our (to-pending patent application Ser. No. 22,334, filed April 14, 1960, now Patent No. 3,099,429, describes and illustrates a mechanism of this kind having a flat port plate interposed between said fiat faces of the cylinder block and po nt block and having apertures permitting the passage of fluid between the ports in the cylinder block and the ports in the port block, said plate being angularly adjustable about the axis of rotation of the cylinder block. The port plate is arranged to be manually adjustable about the axis of rotation to retard the instant of opening of the inlet and outlet ports of a pump so as to promote smoother and quieter running of the pump under increasing load conditions. In a motor, the angular adjustment is arranged to advance the cut-off of the inlet and outlet ports with increase of load. (1" he present invention is an alternative mechanism for angular adjustment of the port plate which effects the adjustment automatically in accordance with operating conditions, and consists essentially of a fluid pressure motor having a working chamber connected to the pump delivery circuit or the motor supply line, which fluid pressure motor is connected to the port plate for angular adjustment thereof against the action of biassing means. Preferably the fluid pressure motor is provided with a re'ciprocable rack or like element which meshes with teeth on the periphery of the port plate. The biassing means may comprise a spring or like resilient bias which urges the port plate to the light load position of adjustment.

Means is preferably provided for smoothing out pulsations in the connection between the working pressure circuit and the port plate adjusting motor.

An external indicator is advantageously coupled to the port plate or its adjusting mechanism toshow the position of adjustment thereof.

A preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FZGURE l is a transverse sectional elevation on the plane containing the port plate of a swash-plate pump;

FIGURE 2 is a longitudinal sectional elevation,

FIGURE 3 is a fragmentary section on the line III-III of FIGURE 1, and

FIGURE 4 is a sectional view on the line IV--IV of FIGURE 1.

The pump consists of a main frame or body F having a front end plate 1 and a ported back end plate or port block 2 carried by the outer cradle 2 through shaft and bushing 3, provided with an oil escape duct 3' which allows any excess oil to escape from the shaft, and through a number of bolts 36 mounted in bushes 3'7 in the end plate 1 and fastened to the cradle 2' by nuts 38. Dowel pins 39 ensure correct register of the end plates -1 and 2 ad, to prevent escape of oil from the body around the junction of the end plates, an O-ring seal 40 isprovided between the end plates. To permit displacement of air from the interior of the body when oil leaks thereinto (it is desirable to operate with the body full of leakage oil), a passage 41 leads through the end plate -1 at the top thereof and connects with a groove 42 in the end plate 2, the groove 42 being connected to atmosphere. Eaclh end plate :1, 2 carrim a journal bearing 4, 5 respectively for a short rigid drive shaft 6. Beyond the bearing 4, an annular seal 43 of rubber or like material is clamped between plates 44 and 45 which compress the seal so that it engages the shaft 6- and prevents escape of oil along the shaft. The plates 44 and 45 do not themselves engage the shaft but only serve to compress the seal 43'. An oil escape duct 46 leads from the inner side of the seal 43 back to the interior of the machine body to return thereto escaping oil trapped by the seal 43. Adjacent the bearing '5 in the back end plate 2, the shaft 6 is formed with a locking taper section 7 on which is locked a cylinder block 8. This block is drawn up on the taper by a back-nut 9 on the shaft. The cylinder block 8 contains a number of cylinders 10 whose axes are mutually inclined inwards towards the back end plate 2. A piston 11 in each cylinder is reciprocable in response to rotation of the shaft 6 and the cylinder block 8 under the control of a normally fixed swash plate 12 carried on conical trunnions 13 (FIG. 4-) by the diametrically opposed lugs 35) integral with swash plate 12. The trunnions have integral flanges 31 spaced from the outer surface of the end plate 1 and connected to the end plate 1 by bolts 47, so that by tightening the bolts 47 the conical tr-unnions can be forced firmly into conical sockets 48 in the lugs 30. Access covers 32 'are provided over the flanges 31. The swash plate 12 has a central conical aperture 14 through which the shaft 6 passes, the dimensions of this aperture being 'sufficient to allow for adjustment of the angle of the swash plate to the shaft 6. The angle of the swash plate 12 is adjusted by the axially movable threaded struts 33 in the shut housings 34 mounted on block 2. Again strut access caps 35 may be provided for adjustment access. A stop 49 is provided for preventing excessive tilt of the swash plate.

The working face of the swash plate is recessed to accommodate an annular slipper plate 16, against which bear slippers 1'7 each of which is engaged with a respective piston 11. For clarity "of illustration in FIGURE 2, only one cylinder 10, piston 11 and slipper 17 is shown.

The back face 1% of the cylinder block 8 is pierced by inlet/outlet ducts 1'9, one to each cylinder 10, the openings to which register successively with arcu-ate inlet and outlet ports 2t 21 in a floating port plate 22 concentric with the shaft 6. This port plate is not anchored to the back end plate 2 except for angular orientation about the shaft '6 with respect to the swash plate 12. This angular orientation is controlled by means described hereinafter. The ports 20, 21 communicate with an external circuit by way of flared ducts 27, 28 respectively (see FIGURE 4) and inlet and outlet sockets 27a, 28a in the back end plate 2. The ports 27, 28 open through a bearing surface 29 on the back end plate to register with the arcuate ports 20, 21, respectively in the port plate 22.

The port plate 22 forms a kind of washer between the mutually opposed faces 18 of the cylinder block 8 and 2? of the back end plate 2, and has a limited freedom to float radially between the two. This radial floating action is hydrostatioally controlled by means of internal ducts and cavities. The port plate 22 also has leakage oil layers between its flat faces and the opposed faces 18 and 29 giving substantially equal and opposite axial loadings on the port plate and thus has a limited freedom to float axially. The port plate is described in greater detail in our co-pending patent application Ser. No. 22,334. The periphery of the port plate has gear teeth '59' formed thereon. With these teeth meshes a cylindrical rack 51 reciprocable on a piston rod 52. The piston rod is transversely located in a guide block 53 and axially adjustable therein by a plunger 54. This plunger is carried in a threaded plug 55 screwed into the pump body, and bears against an adjusting screw 56 threaded into the plug 55.

The guide block 53 has a port (not shown) connected by a pipe shown diagrammatically as 69 to the discharge circuit of the pump (conveniently at the delivery port 21 but elsewhere in the circuit if desired) and opening into the bore for the piston rod 52, and the latter has an annular groove 57 around its circumference which registers with this port over the range of axial adjustment of the piston rod. The groove communicates with an axial oounterbore 58 in the piston rod 52, this counterbore being of enlarged diameter at its inner end to receive an orifice plug 59 having a restricted orifice 60 which opens through the inner end face of the piston rod 52. The bore of the cylindrical rack 51 in which the piston rod 52 is accommodated is blind and constitutes the cylinder of an hydraulic motor by which the rack is moved to displace the port plate 22. Pressure fluid thus follows a path leading from the delivery port 21 along the pipe 69 into the annular groove 57 and thence through the axial counterbore 58 in the piston rod 52 and through the restricted orifice in the plug 59 into the blind bore of the cylindrical rack 51. The pressure of the fluid in said blind bore tends to displace the cylindrical rack 51 against the action of a spring 61 as will now be described.

The rack 51 is loaded by a helical compression spring 61 mounted between the end of the rack and an abutment thimble 62. This thimble is fitted on the end of a pin 63 carried in a threaded plug 64 similar to the plug 55 and axially adjustable therein by means of an abutment screw 65. Adjustment of the axial position of the pin 63 determines the degree of pre-compression of the spring 61 and hence the angular displacement of the port plate 22 by the rack 51 with rise in pressure in the pump delivery circuit. Ihe orifice plug 59 acts as an attenuator to remove or reduce pressure pulses from the control circuit and prevent the port plate being subjected to oscillations at pump frequency and also to prevent resonance with the spring 61.

The angular displacement of the port plate by the rack 51 is in the sense for retarding the opening of both the inlet and the outlet ports 20, 21 and takes place in the same direction as the rotation of the cylinder block. The reason for this is that the inlet pressure in a pump, is low in comparison with the delivery pressure, so that at T.-D.C. of the piston 11 (Le. the completion of the charge stroke), the cylinder contains oil at low pressure. If now the common inlet/outlet duct 19 is opened to the delivery port 21, a pressure surge will be experienced in the cylinder due to the much higher pressure in the load circuit, and a series of shock waves would be set up in the system each time a piston commenced its delivery stroke. Hence, a small angular lag must be provided between T.D.C. and the opening of the duct 19 to the delivery port 21 to allow the oil to be pre-compressed in the cyl inder *10 to at least approximately line pressure. Similarly, 'oil pressure in the cylinders 10 is reduced to at least approximately inlet pressure as they approach the inlet port 20.

Instead of being used as a pump, the machine shown in the drawings may be used as a motor. iln a motor the port in the guide block 53 is connected to the pressure line (i.e. the oil supply line), and the angular displacement of the port plate 22 is in the sense for advancing the cutoff of the outlet or exhaust port 21 (i.e. in the opposite direction to the rotation of the cylinder block) so that oil is trapped in each working cylinder and compressed at B.-D.C. to a pressure nearer the line pressure as load increases. The cylinder is thereby opened to line pressure under conditions of relatively high pressure in the cylinder.

The periphery of the port plate 22 has a second series of gear teeth 50a which mesh with a pinion 66 on the shaft 67 of an external port plate position indicator 68 (see also FIGURE 3) mounted in the back mounting plate 2.

We claim:

1. A swash plate type hydraulic machine comprising a stationary swash plate, a rotatable cylinder block, a plurality of pistons reciprocable in cylinders of said cylinder block under control of the swash plate, ports in a fiat face of the cylinder block communicating with the cylinders therein, a stationary port block having a fiat face, high-pressure and low-pressure ports in said flat face of the port block cooperating with the ports in the cylinder block, a flat port plate interposed between the fiat faces of the cylinder block and the port block and having two apertures respectively permitting the passage of high pressure and low pressure fluid between the ports in the cylinder block and the ports in the port block, said port plate being angul-arly adjustable about the axis of rotation of the cylinder block, teeth on the periphery of said port plate, a fluid pres-sure motor having a cylinder with a blind bore, a piston accommodated in said bore, and an inlet member into said bore, which inlet member has a restricted inlet orifice, a rack driven by said motor and meshing with the teeth on the port plate, a connection between said inlet member and the aforesaid high-pressure port in the port block, a helical compression spring resisting movement of the rack under pressure in the cy-linder, an abutment member against which the end of the spring distant from said motor bears, and adjustment means for adjusting the axial position of said abutment member.

2. A swash plate type hydraulic machine comprising a stationary swash plate, a rotatable cylinder block, a plurality of pistons reciprocable in cylinders of said cylinder block under control of the swash plate, ports in a fiat face of the cylinder block communicating with the cylinders therein, a. stationary port b lock having a flat face, high-pressure and low-pressure ports in said flat face of the port block co-operating with the ports in the cylinder block, a hat port plate interposed between the flat faces of the cylinder block and the port block and having two apertures respectively permitting the passage of high pressure and low pressure fluid between the ports in the cylinder block and the ports in the port block, said port plate being angularly adjustable about the axis of rotation of the cylinder block, teeth on the periphery of said port plate, a fluid pressure motor having a reciprooable cylinder with a blind bore and a stationary piston accommodated in said bore, said piston having an axial fluidinlet passage terminating in a restricted orifice into said bore, a rack carried by said cylinder and meshing with the teeth on the port plate, a connection between said inlet passage of the stationary piston and the aforesaid high-pressure port in the port block, a helical compression spring resisting movement of the cylinder under pressure therein, an abutment member against which the end of the spring distant from said reciprocable cylinder bears, and adjustment means for adjusting the axial position of said abutment member.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Apr. 30, 1958 

1. A SWASH PLATE TYPE HYDRAULIC MACHINE COMPRISING A STATIONARY SWASH PLATE, A ROTATABLE CYLINDER BLOCK, A PLURALITY OF PISTONS RECIPROCABLE IN CYLINDERS OF SAID CYLINDER BLOCK UNDER CONTROL OF THE SWASH PLATE, PORTS IN A FLAT FACE OF THE CYLINDER BLOCK COMMUNICATING WITH THE CYLINDERS THEREIN, A STATIONARY PORT BLOCK HAVING A FLAT FACE, HIGH-PRESSURE AND LOW-PRESSURE PORTS IN SAID FLAT FACE OF THE PORT BLOCK CO-OPERATING WITH THE PORTS IN THE CYLINDER BLOCK, A FLAT PORT PLATE INTERPOSED BETWEEN THE FLAT FACES OF THE CYLINDER BLOCK AND THE PORT BLOCK AND HAVING TWO APERTURES RESPECTIVELY PERMITTING THE PASSAGE OF HIGH PRESSURE AND LOW PRESSURE FLUID BETWEEN THE PORTS IN THE CYLINDER BLOCK AND THE PORTS IN THE PORT BLOCK, SAID PORT PLATE BEING ANGULARLY ADJUSTABLE ABOUT THE AXIS OF ROTATION OF THE CYLINDER BLOCK, TEETH ON THE PERIPHERY OF SAID PORT PLATE, A FLUID PRESSURE MOTOR HAVING A CYLINDER WITH A BLIND BORE, A PISTON ACCOMMODATED IN SAID BORE, AND AN INLET MEMBER INTO SAID BORE, WHICH INLET MEMBER HAS A RESTRICTED INLET ORIFICE, A RACK DRIVEN BY SAID MOTOR AND MESHING WITH THE TEETH ON THE PORT PLATE, A CONNECTION BETWEEN SAID INLET MEMBER AND THE AFORESAID HIGH-PRESSURE PORT IN THE PORT BLOCK, A HELICAL COMPRESSION SPRING RESISTING MOVEMENT OF THE RACK UNDER PRESSURE IN THE CYLINDER, AN ABUTMENT MEMBER AGAINST WHICH THE END OF THE SPRING DISTANT FROM SAID MOTOR BEARS, AND ADJUSTMENT MEANS FOR ADJUSTING THE AXIAL POSITION OF SAID ABUTMENT MEMBER. 